WO2015176077A2

WO2015176077A2 - Systems and methods related to linear and efficient broadband power amplifiers

Info

Publication number: WO2015176077A2
Application number: PCT/US2015/040098
Authority: WO
Inventors: Ramon Antonio Beltran Lizarraga; Aleksey A. Lyalin; Russ Alan Reisner
Original assignee: Skyworks Solutions, Inc.
Priority date: 2014-05-13
Filing date: 2015-07-13
Publication date: 2015-11-19
Also published as: CN106537769B; HK1232345A1; WO2015176077A3; KR20180018984A; KR20230007556A; CN106537769A; KR102618439B1; KR20230005441A; KR102483467B1

Abstract

Systems and methods related to linear and efficient broadband power amplifiers. A power amplifier (PA) system can include an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion. The PA system can further include a Doherty amplifier circuit including a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion. The PA system can further include an output circuit coupled to the Doherty amplifier circuit. The output circuit can include a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal.

Description

SYSTEMS AND METHODS RELATED TO LINEAR AND EFFICIENT

BROADBAND POWER AMPLIFIERS

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Application No. 61/992,842 filed May 13, 2014, entitled SYSTEMS AND METHODS RELATED TO LINEAR AND EFFICIENT BROADBAND POWER AMPLIFIERS, U.S. Provisional Application No. 61/992,843 filed May 13, 2014, entitled CIRCUITS, DEVICES AND METHODS RELATED TO COMBINERS FOR DOHERTY POWER AMPLIFIERS, and U.S. Provisional Application No. 61/992,844 filed May 13, 2014, entitled SYSTEMS AND METHODS RELATED TO LINEAR LOAD MODULATED POWER AMPLIFIERS, the disclosures of which are hereby expressly incorporated by reference herein in their entirety.

BACKGROUND

Field

[0002] The present disclosure generally relates to radio-frequency (RF) power amplifiers (PAs).

Description of the Related Art

[0003] Traditionally, it has been widely believed that the Doherty PA was not suitable for linear PA applications in handsets due to the size, complexity, and non-linear behavior. In fact, in base station applications, predistortion linearizers are typically used with Doherty PAs to meet linearity requirements. As described herein, issues such as size, complexity, and linearity associated with Doherty PAs can be addressed appropriately.

SUMMARY

[0004] In accordance with some implementations, the present disclosure relates to a power amplifier (PA) system including an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion, a Doherty amplifier circuit including a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion, and an output circuit coupled to the Doherty amplifier circuit. The output circuit can include a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal .

[0005] In some embodiments, the PA system can further include a pre- driver amplifier configured to partially amplify the RF signal before reception by the input circuit. In some embodiments, at least one of the input circuit and the output circuit can be implemented as a lumped-element circuit.

[0006] In some embodiments, the carrier amplification path can include a carrier amplifier and the peaking amplification path can include a peaking amplifier, each of the carrier amplifier and the peaking amplifier including a driver stage and an output stage. In some embodiments, the input circuit can include a modified Wilkinson power divider configured to provide DC power to each of the carrier amplifier and the peaking amplifier. In some embodiments, the DC power can be provided to the carrier amplifier and the peaking amplifier through a choke inductance. In some embodiments, each of the carrier amplification path and the peaking amplification path includes a DC blocking capacitance. In some embodiments, the modified Wilkinson power divider can be further configured to provide impedance matching between the driver stages and the pre-driver amplifier. In some embodiments, each of the carrier amplification path and the peaking amplification path can include an LC matching circuit having a capacitance along the path and an inductive coupling to ground.

[0007] In some embodiments, the modified Wilkinson power divider c can be configured to provide a desired phase shifting to compensate or tune for an AM- PM effect associated with the peaking amplifier. In some embodiments, the modified Wilkinson power divider can be further configured to provide a desired attenuation adjustment at an input of either the carrier amplifier or the peaking amplifier to compensate or tune for an AM-AM effect associated with the carrier amplifier and the peaking amplifier. In some embodiments, the modified Wilkinson power divider includes a capacitance that couples a first node along the carrier amplification path to a ground, and an impedance that couples a second node along the peaking amplification path to the ground. In some embodiments, the modified Wilkinson power divider can further include an isolation resistance implemented between the first node and the second node, the isolation resistance selected to prevent or reduce a source-pulling effect between the carrier amplification path and the peaking amplification path.

[0008] In some embodiments, the BALUN circuit can include an LC BALUN transformer. In some embodiments, the peaking amplifier can be configured to behave as a short circuit or a low impedance node when in an off state, and the carrier amplifier can be configured to behave as a single-ended amplifier equivalent to that of a single-section matching network having a series inductance and a shunt capacitance when utilizing the LC BALUN transformer. In some embodiments, the LC BALUN transformer can be configured such that an impedance seen by the carrier amplifier is increased when in a low power mode. In some embodiments, the impedance seen by the carrier amplifier is approximately doubled when in the low power mode.

[0009] In some embodiments, the peaking amplifier can be further configured to operate in a similar manner as a push-pull amplifier where an RF current from the carrier amplifier is influenced by an RF current from the peaking amplifier. In some embodiments, the push-pull operation can reduce even- harmonics thereby improving linearity.

[0010] In some embodiments, the LC BALUN transformer can include a first path that couples an output of the carrier amplifier to an output node, and a second path that couples an output of the peaking amplifier to the output node. In some embodiments, each of the first path and the second path can be inductively coupled to a DC port to provide a DC feed to the output stage. In some embodiments, each of the first path and the second path can include a harmonic trap. In some embodiments, the harmonic trap can include a second harmonic trap having an LC shunt to ground and a series inductance. In some embodiments, the second path can include a shunt capacitance and a series capacitance configured to provide phase compensation for the output of the peaking amplifier. In some embodiments, at least one of the shunt capacitance and the series capacitance can be a surface-mount technology (SMT) capacitor.

[0011] In some embodiments, the LC BALUN transformer can be configured to provide reduced loss in the carrier amplification path to maintain high efficiency at back-off and in a high power mode.

[0012] In some embodiments, load modulation of the peaking amplifier can be configured such that an impedance loci for the peaking amplifier run from an approximately short circuit when the peaking amplifier is in an off state to an optimum load impedance when the peaking amplifier is contributing approximately same power as the carrier amplifier.

[0013] In some embodiments, the input circuit can be a broadband circuit at least in part due to a lead-lag network configured to provide broadband phase shift.

[0014] In some embodiments, the input circuit is configured to provide reactive to real impedance matching, and isolation between the carrier amplifier and peaking amplifier, while providing broadband performance.

[0015] In some implementations, the present disclosure relates to a method for amplifying a radio-frequency (RF) signal, the method including providing a Doherty amplifier circuit having a carrier amplification path and a peaking amplification path, receiving an RF signal, splitting the RF signal into a first portion and a second portion, the first portion provided to the carrier amplification path, the second portion provided to the peaking amplification path, and combining, using a balance to unbalance (BALUN) circuit, outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal.

[0016] In some implementations, the present disclosure relates to a power amplifier module. The power amplification module can include a packaging substrate configured to receive a plurality of components and a power amplifier (PA) system implemented on the packaging substrate. The PA system can include an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion. The PA system can further include a Doherty amplifier circuit having a carrier amplification path coupled to the input to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion. The PA system can further include an output circuit coupled to the Doherty amplifier circuit. The output circuit can include a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal. The power amplification module can further include a plurality of connectors configured to provide electrical connections between the PA system and the packaging substrate.

[0017] In some implementations, the present disclosure relates to a wireless device including a transceiver configured to generate a radio-frequency signal, a power amplification (PA) module in communication with the transceiver, and an antenna in communication with the PA module, the antenna configured to facilitate transmission of the amplified RF signal. The PA module can include an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion. The PA module can further include a Doherty amplifier circuit having a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion. The PA module can further include an output circuit coupled to the Doherty amplifier circuit. The output circuit can include a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal. The transceiver can further include an antenna, in communication with the PA module, configured to facilitate transmission of the amplified RF signal.

[0018] In accordance with some implementations, the present disclosure relates to a signal combiner including a balun transformer circuit having a first coil and a second coil. The first coil is implemented between a first port and a second port. The second coil is implemented between a third port and a fourth port. The first port and the third port are coupled by a first capacitance. The second port and the fourth port are coupled by a second capacitance. The first port is configured to receive a first signal. The fourth port is configured to receive a second signal. The second port is configured to yield a combination of the first signal and the second signal. The signal combiner further includes a termination circuit that couples the third port to a ground.

[0019] In some embodiments, the first port can be configured to receive a carrier-amplified signal from a Doherty power amplifier (PA) and the fourth port can be configured to receive a peaking-amplified signal from the Doherty PA. In some embodiments, the termination circuit can include a capacitor. In some embodiments, the capacitor can have a capacitance approximately equal to a multiplicative inverse of two times pi times an operating frequency of the Doherty PA times a characteristic impedance of a load coupled to the Doherty PA.

[0020] In some embodiments, the first port can be configured to receive a peaking-amplified signal from a Doherty power amplifier (PA) and the fourth port is configured to receive a carrier-amplified signal from the Doherty PA. In some embodiments, the termination circuit can include an inductor. In some embodiments, the inductor can have an inductance approximately equal to a characteristic impedance of a load coupled to the Doherty PA divided by two time pi times an operating frequency of the Doherty PA.

[0021] In some embodiments, an S-parameter between a first one of the ports and a second one of the ports can be approximately equal to (1 +j)/2. In some embodiments, an S-parameter between a first one of the ports and second one of the ports can be approximately equal to (1 -j)/2. In some embodiments, an S- parameter matrix of S-parameters between the ports can only include values of approximately 0, (1 +j)/2, and (1 -j)/2.

[0022] In some embodiments, the balun transformer circuit can be implemented as an integrated passive device. In some embodiments, the integrated passive device further implements an auto-transformer based impedance matching circuit.

[0023] In some implementations, the present disclosure relates to a power amplifier module including a packaging substrate configured to receive a plurality of components and a signal combiner implemented on the packaging substrate. The signal combiner includes a balun transformer circuit having a first coil and a second coil. The first coil is implemented between a first port and a second port. The second coil is implemented between a third port and a fourth port. The first port and the third port are coupled by a first capacitance. The second port and the fourth port are coupled by a second capacitance. The first port is configured to receive a first signal. The fourth port is configured to receive a second signal. The second port is configured to yield a combination of the first signal and the second signal. The signal combiner further includes a termination circuit that couples the third port to a ground.

[0024] In some embodiments, the balun transformer circuit can be implemented as an integrated passive device. In some embodiments, the integrated passive device can further implement an auto-transformer based impedance matching circuit.

[0025] In some embodiments, the PA module can further include a Doherty PA implemented on the packaging substrate. The Doherty PA can have a carrier amplification path yielding a carrier-amplified signal and a peaking amplification path yielding a peaking-amplified signal. In some embodiments, the first port can be configured to receive the carrier-amplified signal and the fourth port can be configured to receive the peaking-amplified signal. In some embodiments, the termination circuit can include a capacitor having a capacitance approximately equal to a multiplicative inverse of two times pi times an operating frequency of the Doherty PA times a characteristic impedance of a load coupled to the Doherty PA. In some embodiments, the first port can be configured to receive the peaking-amplified signal and the fourth port can be configured to receive the carrier-amplified signal. In some embodiments, the termination circuit can include an inductor having an inductance approximately equal to a characteristic impedance of a load coupled to the Doherty PA divided by two time pi times an operating frequency of the Doherty PA.

[0026] In some embodiments, an S-parameter matrix of S-parameters between the ports only includes values of approximately 0, (1 +j)/2, and (1 -j)/2.

[0027] In some implementations, the present disclosure relates to a wireless device including a transceiver configured to generate a radio-frequency (RF) signal. The wireless device further includes a power amplifier (PA) module in communication with the transceiver. The PA module includes an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion. The PA module further includes a Doherty PA having a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion. The PA module further includes an output circuit coupled to the Doherty amplifier circuit. The output circuit includes a balun transformer circuit having a first coil and a second coil. The first coil is implemented between a first port and a second port. The second coil is implemented between a third port and a fourth port. The first port and the third port are coupled by a first capacitance. The second port and the fourth port are coupled by a second capacitance. The first port is configured to receive a first signal via the carrier amplification path. The fourth port is configured to receive a second signal via the peaking amplification path. The second port is configured to yield a combination of the first signal and the second signal as an amplified RF signal. The wireless device further includes an antenna in communication with the PA module. The antenna is configured to facilitate transmission of the amplified RF signal.

[0028] In some implementations, the present disclosure relates to a method for amplifying a radio-frequency (RF) signal. The method includes providing a Doherty amplifier circuit having a carrier amplification path and a peaking amplification path, receiving an RF signal, splitting the RF signal into a first portion and a second portion, the first portion provided to the carrier amplification path, the second portion provided to the peaking amplification path, and combining, using a balun transformer circuit, an output of the carrier amplification path and an output of the peaking amplification path to yield an amplified RF signal. The balun transformer circuit includes a first coil and a second coil. The first coil is implemented between a first port and a second port. The second coil is implemented between a third port and a fourth port. The first port and the third port are coupled by a first capacitance. The second port and the fourth port are coupled by a second capacitance. The first port is configured to receive the output of the carrier amplification path. The fourth port is configured to receive the output of the peaking amplification path. The second port is configured to yield the amplified RF signal.

[0029] In accordance with some implementations, the present disclosure relates to a power amplifier (PA) system including an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion. The PA system further includes a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion. The first portion and the second portion having different phases and different powers. The PA system further includes an output circuit coupled to the Doherty amplifier circuit. The output circuit is configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal.

[0030] In some embodiments, the input circuit can include a phase-shifter configured to cause the first portion and the second portion to have different phases. In some embodiments, the phase-shifter and peaking amplifier can be implemented in a peaking amplification path. In some embodiments, the first portion and second portion can be out-of-phase by between 10 degrees and 20 degrees. In some embodiments, the different phases can reduce at least one of AM/AM distortion or AM/PM distortion as compared to equal phases.

[0031] In some embodiments, the input circuit can include an attenuator configured to cause the first portion and the second portion to have different powers. In some embodiments, the attenuator and the carrier amplifier can be implemented in a carrier amplification path. In some embodiments, the different powers can reduce at least one of AM/AM distortion or AM/PM distortion as compared to equal powers.

[0032] In some embodiments, the input circuit can include a pre-driver amplifier.

[0033] In some embodiments, the peaking amplifier includes a driver stage configured to operate in a first biasing mode and an output stage configured to operate in a first biasing mode. In some embodiments, the first biasing mode is a Class B biasing mode. In some embodiments, the Class B biasing mode increases the PAE of the peaking amplifier as compared to a Class AB biasing mode. In some embodiments, the carrier amplifier includes a driver stage configured to operate in a second biasing mode. In some embodiments, the second biasing mode is a Class AB biasing mode. In some embodiments, the carrier amplifier further includes an output stage configured to operate in the first biasing mode. In some embodiments, the carrier amplifier further includes an output stage configured to operate in the second biasing mode.

[0034] In some implementations, the present disclosure relates to a power amplifier (PA) module. The PA module includes a packaging substrate configured to receive a plurality of components and a PA system implemented on the packaging substrate. The PA system includes an input circuit configured to receive a radio- frequency (RF) signal and split the RF signal into a first portion and a second portion. The PA system further includes a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion. The first portion and the second portion have different phases and different powers. The PA system further includes an output circuit coupled to the Doherty amplifier circuit. The output circuit is configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal.

[0035] In some embodiments, at least one of the input circuit or the output circuit can be implemented as an integrated passive device. In some embodiments, at least one of the input circuit or the output circuit can be implemented on a single GaAs die.

[0036] In some implementations, the present disclosure relates to a wireless device. The wireless device includes a transceiver configured to generate a radio-frequency (RF) signal. The wireless device includes a power amplifier (PA) module in communication with the transceiver. The PA module includes an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion. The PA module includes a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion. The first portion and the second portion have different phases and different powers. The PA module includes an output circuit coupled to the Doherty amplifier circuit. The output circuit is configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal. The wireless device further includes an antenna in communication with the PA module. The antenna is configured to facilitate transmission of the amplified RF signal.

[0037] In some implementations, the present disclosure relates to a method for amplifying a radio-frequency (RF) signal. The method includes providing a Doherty amplifier circuit having a carrier amplification path and a peaking amplification path, receiving an RF signal, splitting the RF signal into a first portion and a second portion, the first portion provided to the carrier amplification path, the second portion provided to the peaking amplification path, the first portion and the second portion having different phases and different powers, and combining an output of the carrier amplification path and an output of the peaking amplification path to yield an amplified RF signal.

[0038] For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the inventions have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 shows that in some embodiments, a power amplifier can be implemented as a linear and efficient broadband power amplifier.

[0040] Figure 2 shows an example architecture of a power amplifier including a carrier amplification path and a peaking amplification path.

[0041] Figure 3 shows an example configuration of a modified Wilkinson- type power divider. [0042] Figure 4 shows an example configuration of a combiner that can provide balance to unbalance (BALUN) transformer functionality.

[0043] Figure 5 shows first example load modulation profiles of a carrier amplifiers and peaking amplifier using a BALUN transformer configuration.

[0044] Figure 6 shows second example load modulation profiles of a carrier amplifiers and peaking amplifier using a BALUN transformer configuration.

[0045] Figure 7 shows an example configuration of a power amplifier including a modified Wilkinson-type power divider.

[0046] Figure 8 shows an example broadband phase shift response.

[0047] Figure 9 shows example impedance responses including harmonic traps.

[0048] Figure 10 shows example adjacent channel leakage-power ratio (ACLR) curves and power-added efficiency (PAE) curves.

[0049] Figure 1 1 depicts a wireless device having one or more features described herein.

[0050] Figure 12 shows an example combiner configuration in which both a carrier amplifier and a peaking amplifier are in an on state.

[0051] Figure 13 shows an example combiner configuration in which a carrier amplifier is in an on state and a peaking amplifier is in an off state.

[0052] Figure 14 shows an example Doherty combiner that includes two or more quarter wave transmission lines.

[0053] Figure 15 shows an example Smith chart for the combiner of Figure

14.

[0054] Figure 16 shows an example Doherty combiner that includes a 3 dB coupler.

[0055] Figure 17 shows an example Smith chart for the combiner of Figure

16.

[0056] Figure 18 shows an example hybrid circuit that can be utilized as a Doherty combiner.

[0057] Figure 19 shows another example hybrid circuit that can be utilized as a Doherty combiner. [0058] Figure 20 shows an example S-parameter matrix for the combiner of Figure 16.

[0059] Figure 21 shows an example S-parameter matrix for the combiner of Figure 18.

[0060] Figure 22 shows an example Doherty combiner configuration that utilizes the hybrid circuit of Figure 18.

[0061] Figure 23 shows impedance trajectories resulting from Doherty action in the combiner of Figure 22.

[0062] Figure 24 shows another example Doherty combiner configuration that utilizes the hybrid circuit of Figure 18.

[0063] Figure 25 shows an example of integration of a hybrid circuit and an auto-transformer based impedance matching as an integrated passive device (IPD).

[0064] Figure 26 shows an example Smith chart with an inverted load- modulation trajectory.

[0065] Figure 27 shows another example of integration of a hybrid circuit as an IPD.

[0066] Figure 28 shows an example architecture of a power amplifier in which a Doherty combiner having one or more features as described herein can be implemented.

[0067] Figure 29 depicts a wireless device having one or more features described herein.

[0068] Figure 30 shows an example architecture of a power amplifier (PA) having one or more features as described herein.

[0069] Figure 31 shows an example of a combiner circuit for a Doherty PA.

[0070] Figure 32 shows an example of a splitter circuit for a Doherty PA.

[0071] Figure 33 shows an example of a power splitter that can be utilized as the divider of Figure 30.

[0072] Figure 34 shows another example of a power splitter that can be utilized as the divider of Figure 30. [0073] Figure 35 shows an example of a combiner that can be utilized as the combiner of Figure 30.

[0074] Figure 36 shows another example of a combiner that can be utilized as the combiner of Figure 30.

[0075] Figure 37 shows an example of a low headroom Class AB bias circuit.

[0076] Figure 38 shows an example of a low headroom Class B bias circuit.

[0077] Figure 39 shows an example of a beneficial effect of utilizing a Class B biasing of the driver stage for a peaking amplifier.

[0078] Figure 40 shows another example of a beneficial effect of utilizing a Class B biasing of the driver stage for a peaking amplifier.

[0079] Figure 41 shows an example of linearization effect that can be obtained by introducing a phase shift between the RF signals associated with carrier amplification and peaking amplification.

[0080] Figure 42 shows an example of linearization effect that can be obtained by introducing an uneven power split between the RF signals associated with carrier amplification and peaking amplification.

[0081] Figure 43 shows an example of combined linearization effect that can be obtained by a combination of the phase shift and uneven power split.

[0082] Figure 44 shows example plots of power-added efficiency (PAE) and adjacent channel power (ACP) at various operating frequencies for a front-end module (FEM).

[0083] Figure 45 depicts a wireless device having one or more features described herein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0084] The headings provided herein, if any, are for convenience only and do not necessarily affect the scope or meaning of the claimed invention. Described herein are systems, devices, circuits and methods related to radio-frequency (RF) power amplifiers (PAs). Power Amplification Using a Balun Transformer

[0085] Figure 1 shows that in some embodiments, a PA 100 having one or more features as described herein can be configured to provide broadband capability with either or both of desirable linearity and efficiency. The PA 100 is shown to receive an RF signal (RFJN) and generate an amplified signal (RF_OUT). Various examples related to such a PA are described herein in greater detail.

[0086] Figure 2 shows an example architecture of a PA 100 having one or more features as described herein. The architecture shown is a Doherty PA architecture. Although the various examples are described in the context of such a Doherty PA architecture, it will be understood that one or more features of the present disclosure can also be implemented in other types of PA systems.

[0087] The example PA 100 is shown to include an input port (RFJN) for receiving an RF signal to be amplified. Such an input RF signal can be partially amplified by a pre-driver amplifier 102 before being divided into a carrier amplification path 1 10 and a peaking amplification path 130. Such a division can be achieved by a divider 104. Examples related to the divider 104 are described herein in greater detail, including examples in reference to Figures 3 and 7.

[0088] In Figure 2, the carrier amplification path 1 10 is shown to include an attenuator 1 12 and amplification stages collectively indicated as 1 14. The amplification stages 1 14 are shown to include a driver stage 1 16 and an output stage 120. The driver stage 1 16 is shown to be biased by a bias circuit 1 18, and the output stage 120 is shown to be biased by a bias circuit 122. In some embodiments, there may be more or less number of amplification stages. In various examples described herein, the amplification stages 1 14 are sometimes described as an amplifier; however, it will be understood that such an amplifier can include one or more stages.

[0089] In Figure 2, the peaking amplification path 130 is shown to include phase shifting circuit 132 and amplification stages collectively indicated as 134. The amplification stages 134 are shown to include a driver stage 136 and an output stage 140. The driver stage 136 is shown to be biased by a bias circuit 138, and the output stage 140 is shown to be biased by a bias circuit 142. In some embodiments, there may be more or less number of amplification stages. In various examples described herein, the amplification stages 134 are sometimes described as an amplifier; however, it will be understood that such an amplifier can include one or more stages.

[0090] Figure 2 further shows that the carrier amplification path 1 10 and the peaking amplification path 130 can be combined by a combiner 144 so as to yield an amplified RF signal at an output port (RF_OUT). Examples related to the combiner 144 are described herein in greater detail, including examples in reference to Figures 4 and 7.

[0091] In some embodiments, the divider 104 of Figure 2 can be implemented as a lumped-element power splitter. Such a power splitter can be implemented as a modified Wilkinson-type power divider configured to provide DC power to each of the driver stages (e.g., 1 16, 136 in Figure 2). Figure 3 shows an example configuration of a modified Wilkinson-type power divider 104 that can be implemented as the divider 104 of Figure 2. Figure 7 shows an example of how the modified Wilkinson-type power divider 104 can be implemented in a circuit example of the PA 100 of Figure 2.

[0092] In Figure 3, the modified power divider 104 is shown to include an input port 150 configured to receive an input RF signal. As shown in the example PA circuit 100 of Figure 7, the input port 150 can be coupled to a collector of a transistor Q0 of a pre-driver amplifier 102. The input port 150 is further shown to be coupled to a splitter node 156 through node 152. The node 152 is shown to be coupled to a DC supply port 154 through an inductance L1 (e.g., an inductor). The DC power for each of the driver stages can be obtained through the DC supply port 154. In Figure 3, L1 can be part of the modified Wilkinson-type splitter which matches the impedance looking into the splitter to the impedance presented to the pre-driver PA collector. At the same time, L1 can serve as a DC path for the pre- driver.

[0093] In Figure 3, the carrier amplification path (1 10 in Figure 2) is shown to include a path from the splitter node 156 to node 160, through a capacitance C1 , node 158, and a capacitance C3. The node 160 may or may not be connected to a port 162 to facilitate coupling of the foregoing path to a carrier amplifier (e.g., 1 14 in Figure 2). The node 158 is shown to be coupled to ground through a capacitance C2. The node 160 is shown to be coupled to ground through an inductance L2.

[0094] In Figure 3, the peaking amplification path (130 in Figure 2) is shown to include a path from the splitter node 156 to node 166, through a capacitance C4, node 164, and a capacitance C5. The node 166 may or may not be connected to a port 168 to facilitate coupling of the foregoing path to a peaking amplifier (e.g., 134 in Figure 2). The node 164 is shown to be coupled to ground through an inductance L3. The node 166 is shown to be coupled to ground through an inductance L4.

[0095] In Figure 3, a resistance R1 is shown to couple the node 158 of the carrier amplification path and the node 164 of the peaking amplification path. The resistance R1 can be selected to function as an isolation resistor to prevent or reduce source-pulling effect(s) from the carrier and/or peaking amplifiers.

[0096] In Figure 3, the capacitance C1 can be selected to provide DC blocking functionality for the carrier amplification path. Similarly, the capacitance C4 can be selected provide DC blocking functionality for the peaking amplification path.

[0097] In Figure 3, the capacitance C3 and the inductance L2 can be selected to provide impedance matching between the pre-driver amplifier (e.g., 102 in Figures 2 and 7) and the carrier amplifier 1 14. Similarly, the C5 and the inductance L4 can be selected to provide impedance matching between the pre- driver amplifier (e.g., 102 in Figures 2 and 7) and the peaking amplifier 134.

[0098] In Figure 3, the capacitance C2 associated with the carrier amplification path and the inductance L3 associated with the peaking amplification path can be selected to provide a desired phase shifting between the two paths. Such a phase shift can be selected to, for example, compensate for and/or tune AM- PM phenomena associated with the peaking amplifier 134. In Figure 2, such a phase-shifting functionality is depicted as block 132 along the peaking amplification path 130.

[0099] In some embodiments, and as shown in Figure 2, an attenuator 1 12 can be provided along either the carrier amplification path 1 10 (e.g., before the carrier amplifier 1 14) or the peaking amplification path 130 (e.g., before the peaking amplifier 134). Such an attenuator can be configured to provide a desired attenuation adjustment to compensate for and/or tune AM-AM phenomena associated with either or both of the carrier and peaking amplifiers. Such an attenuator can also promote uneven power splitting between the two amplification paths.

[0100] It is noted that the foregoing corrections and/or tuning of the AM- AM and/or AM-PM effects can result in the PA 100 of Figures 2 and 7 to be substantially linear. Such linearity can be achieved without requiring digital pre- distortion which typically reduces efficiency of the PA system and applicability of the PA system in amplifiers for portable wireless devices. Further, linearity achieved by the PA 100 of Figures 2 and 7 (without the digital pre-distortion) can be similar to linearity performance associated with a class-AB single-ended amplifier.

[0101] In some embodiments, the combiner 144 of Figure 2 can be implemented as or similar to a lumped-element balanced to unbalanced (BALUN) transformer. Figure 4 shows an example configuration of a combiner 144 that can provide such BALUN transformer functionality. Figure 7 shows an example of how the combiner 144 can be implemented in a circuit example of the PA 100 of Figure 2.

[0102] In Figure 4, the combiner 144 is shown to include a portion of the carrier amplification path (e.g., 1 10 in Figure 2) and a portion of the peaking amplification path (130) joined at a combining node 186. The combining node 186 is shown to be coupled to an output port 198 (RF_OUT in Figures 2 and 7).

[0103] In Figure 4, the portion of the carrier amplification path is shown to couple the combining node 186 and node 182 through an inductance L13. The node 182 may or may not be connected to a port 180 to facilitate coupling of the foregoing path to a carrier amplifier (e.g., 1 14 in Figure 2). The node 182 is shown to be coupled to ground through a capacitance C1 1 and an inductance L12. The node 182 is also shown to be coupled to a port 184 through an inductance L1 1 .

[0104] In Figure 4, the portion of the peaking amplification path is shown to couple the combining node 186 and node 192 through an inductance L16, node 196, and a capacitance C14. The node 192 may or may not be connected to a port 190 to facilitate coupling of the foregoing path to a peaking amplifier (e.g., 134 in Figure 2). The node 192 is shown to be coupled to ground through a capacitance C12 and an inductance L15. The node 192 is also shown to be coupled to a port 194 through an inductance L14. The node 196 is shown to be coupled to ground through a capacitance C13.

[0105] In Figure 4, the node 182 can be coupled to the collector of the output stage (e.g., 120 in Figure 2) of the carrier amplifier (1 14) through the port 180. Accordingly, DC feed can be provided to the output stage (120) of the carrier amplifier (1 14) through the port 184 and the inductance L1 1 . Similarly, the node 192 can be coupled to the collector of the output stage (e.g., 140 in Figure 2) of the peaking amplifier (134) through the port 190. Accordingly, DC feed can be provided to the output stage (140) of the peaking amplifier (134) through the port 194 and the inductance L14.

[0106] In Figure 4, the capacitance C1 1 , the inductance L12, and the inductance L13 can be selected to function as a second harmonic trap for the output of the carrier amplifier (1 14). Similarly, the capacitance C12, the inductance L15, and the inductance L16 can be selected to function as a second harmonic trap for the output of the peaking amplifier (134).

[0107] In Figure 4, the capacitance C13 and the capacitance C14 can be selected to provide phase compensation for the output of the peaking amplifier (134). In some embodiments, C13 and C14 can be implemented as surface-mount technology (SMT) capacitors. In such embodiments, using as little as two SMT capacitors, the combiner 144 can be implemented as a broadband power combiner.

[0108] The example combiner 144 of Figure 4 can provide desirable functionalities for operations of Doherty PA architectures. For example, the peaking amplifier in a Doherty PA architecture is typically required to behave as a short circuit or a very low impedance path when it is turned off, and the carrier amplifier typically acts as a single-ended amplifier with an equivalent circuit that is similar to or the same as a typical single-section matching network (e.g., series L and shunt C) when using an LC BALUN configuration. In such a state, impedance seen by the carrier amplifier can be doubled.

[0109] When the peaking amplifier is turned on, the PA system can operate in a manner similar to a "push-pull" amplifier. For example, the RF current from the carrier amplifier can see the current from the peaking amplifier. In such a state, linearity can be improved since the even harmonic content can be reduced.

[0110] As described herein, the combiner 144 with the example LC BALUN configuration can be implemented in a compact form, using as little as two SMT components (e.g., capacitors). Such a combiner can be configured to provide impedance matching from, for example, a 50-Ohm output to transistor-collectors of the peaking and carrier amplifiers, including RF chokes and harmonic traps.

[0111] As described herein, the combiner 144 with the example LC BALUN configuration can be implemented to reduce the loss in the carrier amplifier path compared to other Doherty topologies. Such a feature in turn can facilitate maintenance of high efficiency at back-off and high power modes. Further, the LC BALUN configuration can provide required or desired impedance and phase adjustment for the carrier amplifier. Such a feature can be important when designing an asymmetric loaded Doherty transmitter.

[0112] In some embodiments, load modulation associated with a peaking amplifier as described herein is generally opposite as in conventional Doherty transmitters. Figure 5 shows load modulation profiles for carrier (200) and peaking (202) amplifiers of a conventional Doherty transmitter using a BALUN transformer configuration. Figure 6 shows load modulation profiles for carrier (204) and peaking (206) amplifiers of a Doherty transmitter using a BALUN transformer configuration as described herein (e.g., Figure 7). For the peaking amplifiers in Figures 5 and 6, one can see that impedance loci run in opposite directions from their respective short circuit states (e.g., when the peaking amplifier is turned off) to their respective optimum load impedance conditions (e.g., when the peaking amplifier is contributing same power as the carrier amplifier). For the conventional example of Figure 5, the impedance loci of the peaking amplifier run in the same direction as that of the carrier amplifier as power is increased. For the example of Figure 6, the impedance loci of the peaking amplifier run in the opposite direction as that of the carrier amplifier as power is increased.

[0113] Figure 7 shows an example of a PA 100 having one or more features as described herein. The PA can include a pre-driver amplifier 102 such as a one-stage single-ended amplifier. The output of the pre-driver amplifier 102 is shown to be provided to a divider 104, such as the example described in reference to Figure 3. The divided outputs of the divider 104 are shown to be provided to a carrier amplifier 1 14 and a peaking amplifier 134. The outputs of the carrier amplifier 1 14 and the peaking amplifier 134 are shown to be combined by a combiner 144, such as the example described in reference to Figure 4.

[0114] In the example PA 100 of Figure 7, the divider 104 and the combiner 144 can yield a broadband combination. For example, the divider 104 is broadband in nature due to, for example, the lead-lag network that provides broadband phase shift. An example of such a phase shift response is shown as curve 250 in Figure 8. The example response curve 250 is representative of a typical phase difference between the matching reactive base impedances and the driver amplifier collector. It is further noted that the divider 104 provides advantageous features such as reactive to real impedance matching, isolation between carrier and peaking amplifiers, and still yield broadband performance.

[0115] In another example, the combiner 144 with its LC BALUN configuration can also contribute to the broadband performance of the PA 100. As described herein, the LC BALUN can include harmonic traps configured to keep the impedance locus within lower constant Q circles. Example of such impedance responses are shown as curves 260, 262, 264 in Figure 9. The example response curves 260, 262, 264 are representative of collector load impedance vs. frequency for different ZP values. ZP1 represents the load impedance seen by carrier PA collector when both carrier and peaking PAs are turned on (in operation) and it is about 5.7+j0.1 19 Ohms in the example. ZP2 is the collector impedance at the peaking PA collector which is similar to the previous case (e.g., same impedance when both PAs are on). ZP4 is the impedance seen by carrier PA collector when peaking PA is off which is effectively doubled to around 10.86+j0.058 Ohms in the example. Such a feature effectively enhances the PA architecture bandwidth, since the impedances vs. frequency are not spread along the Smith chart.

[0116] A PA architecture having one or more features as described herein, including the examples of Figures 1 -4 and 7, can be configured to yield excellent linear and efficient broadband performance. For example, a 21 % relative bandwidth can be achieved for -37-dBc ACLR (adjacent channel leakage-power ratio) using an LTE signal (e.g., 10-MHz BW, QPSK, 12 RB). Figure 10 shows ACLR curves and power-added efficiency (PAE) curves for different samples. The upper set of curves (270, 292) are for power added efficiency (PAE) for 27.5 and 27 dBm output power levels, respectively. The middle set of curves (274, 276) are for ACLR1 for 27.5 and 27 dBm output power levels, respectively. The dashed curve (278) is for ACLR2 for 27.5 dBm output power. In the context of ACLR performance, one can see that the - 37-dBc ACLR bandwidth at 27-dBm output power is approximately 525 MHz (e.g., between markers "m39" and "m38") which is approximately 21 % of the center frequency of approximately 2,500 MHz (e.g., marker "m48). It is noted that bandwidth can be even wider if the ACLR level is allowed to increase.

[0117] In some implementations, a device and/or a circuit having one or more features described herein can be included in an RF device such as a wireless device. Such a device and/or a circuit can be implemented directly in the wireless device, in a modular form as described herein, or in some combination thereof. In some embodiments, such a wireless device can include, for example, a cellular phone, a smart-phone, a hand-held wireless device with or without phone functionality, a wireless tablet, etc.

[0118] Figure 1 1 schematically depicts an example wireless device 400 having one or more advantageous features described herein. In the example, one or more PAs 1 10 collectively indicated as a PA architecture 100 can include one or more features as described herein. Such PAs can facilitate, for example, multi-band operation of the wireless device 400.

[0119] The PAs 1 10 can receive their respective RF signals from a transceiver 410 that can be configured and operated to generate RF signals to be amplified and transmitted, and to process received signals. The transceiver 410 is shown to interact with a baseband sub-system 408 that is configured to provide conversion between data and/or voice signals suitable for a user and RF signals suitable for the transceiver 410. The transceiver 410 is also shown to be connected to a power management component 406 that is configured to manage power for the operation of the wireless device 400. Such power management can also control operations of the baseband sub-system 408 and the Pas 1 10.

[0120] The baseband sub-system 408 is shown to be connected to a user interface 402 to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system 408 can also be connected to a memory 404 that is configured to store data and/or instructions to facilitate the operation of the wireless device 400, and/or to provide storage of information for the user.

[0121] In the example wireless device 400, outputs of the PAs 1 10 are shown to be matched (via match circuits 420) and routed to an antenna 416 via their respective duplexers 412a-412d and a band-selection switch 414. The band- selection switch 414 can be configured to allow selection of an operating band. In some embodiments, each duplexer 412 can allow transmit and receive operations to be performed simultaneously using a common antenna (e.g., 416). In Figure 1 1 , received signals are shown to be routed to "Rx" paths (not shown) that can include, for example, a low-noise amplifier (LNA).

[0122] A number of other wireless device configurations can utilize one or more features described herein. For example, a wireless device does not need to be a multi-band device. In another example, a wireless device can include additional antennas such as diversity antenna, and additional connectivity features such as Wi-Fi, Bluetooth, and GPS.

Signal Combining using a Coiled Balun Transformer

[0123] A combiner can be implemented as part of a Doherty PA, and is typically utilized to provide a number of functions. For example, a combiner can be configured to provide equal power combining when the PA operates at full power. Figure 12 shows an example of such a configuration where the combiner can act as a conventional power combiner. In Figure 12, values of various performance and operating parameters are examples; and can be adjusted appropriately for different applications.

[0124] Thus, in Figure 12, a configuration 2100 is illustrated in which both a carrier amplifier 21 10 and a peaking amplifier 21 12 are in an on state. In some implementations, the both the carrier amplifier 21 10 and the peaking amplifier are saturated and have a power-added efficiency (PAE) of 50% or greater. The outputs of the carrier amplifier 21 10 and the peaking amplifier 21 12 are fed to respective input ports 2131 , 2132 of a transmission line combiner 2120. At both the first input port 2131 and the second input port 2132, an impedance of 50 Ohms may be presented. The transmission line combiner 2120 includes a 50-Ohm transmission line 2121 coupled between the first input port 2131 and the second input port 2132 and a 35.5-Ohm transmission line 2122 coupled between the second input port 2132 and an output port 2133. The input of the 35.5-Ohm transmission line 2122 may present an impedance of 25 Ohms.

[0125] In another example, a combiner can be configured to provide impedance transformation between the PA and the load coupled to the PA. For example, a 2:1 impedance transformation can be implemented from the load to the output of the carrier amplifier when the peaking amplifier is idle. Such a transformation functionality is shown in Figure 13. Again, values of various performance and operating parameters are examples; and can be adjusted appropriately for different applications. The foregoing functionality can be desirable over as broad as possible fractional bandwidth in order to achieve economical coverage of multiple operating frequencies with one amplifier.

[0126] Thus, in Figure 13, a configuration 2150 is illustrated in which the carrier amplifier 21 10 is in an on state and the peaking amplifier 21 12 is in an off state. In some implementations, the carrier amplifier 21 10 is saturated and has a PAE of 50% or greater. In such a configuration 2150, an impedance of 100 Ohms may be presented at the first input port 2131 and a very high impedance (a near open) may be presented at the second input port 2132. [0127] Figure 14 shows an example of a common Doherty combiner 2120 that includes two or more quarter wave transmission lines 2121 , 2122 set up in such a way that both combining and impedance transformation functions are achieved. Such an implementation is typically relatively bulky, especially at low frequency. Accordingly, such a combiner 2120 may not be particularly suitable for applications in devices such as RFIC (radio-frequency integrated circuit), MMIC (monolithic microwave integrated circuit), and other RF modules. Impedance spread vs. frequency for the Doherty combiner 2120 of Figure 14 is shown in an example Smith chart 2144 of Figure 15.

[0128] Other types of Doherty combiners can be based on lumped elements. Most of such implementations are limited to relatively narrow bands of operation.

[0129] Figure 16 shows another example of a Doherty combiner 2220 that utilizes a 3 dB coupler 2221 with near open termination impedance at an isolation port 2222. Even though such an implementation is more compact than the example combiner 2120 of Figure 14, it is still typically too large for applications such as RFIC, MMIC and other RF modules, at low frequency due to its quarter wave length. The combiner 2220 includes a 3 db coupler 2221 having a first port coupled to a first input port 2231 of the combiner 2220, a second port coupled to a second input port 2232 of the combiner 2220, a third port coupled to an output port 2233 of the combiner 2220, and a fourth port (e.g., isolation port 2222) coupled to a near open termination impedance. Impedance spread vs. frequency for the Doherty combiner 2220 of Figure 16 is shown in an example Smith chart 2244 of Figure 17.

[0130] Figures 18 and 19 show an example of a hybrid circuit that can be utilized as a Doherty combiner. Such a hybrid circuit can be configured to be particularly suitable for applications such as RFIC, MMIC and other RF modules. Figure 18 shows a schematic representation of such a hybrid circuit, and Figure 19 shows an example layout of the same.

[0131] The hybrid circuit of Figures 18 and 19 can be implemented as a semi-lumped 90 degree hybrid based on balun. Due to the compact nature of the balun used, such a design can be easily implemented on insulating/semi-insulating substrates such as silicon, GaAs and IPD (e.g., glass or silicon).

[0132] In the hybrid circuit of Figures 18 and 19, values of various performance and operating parameters are examples; and can be adjusted appropriately for different applications.

[0133] Thus, in Figure 18, a signal combiner 2320 is shown including a first port 2331 , a second port 2332, a third port 2333, and fourth port 2334. A first capacitor 2322 couples the first port 2331 and the second port 2332. A second capacitor 2323 couples the third port 2333 and the fourth port 2334. The signal combiner 2320 also includes a transformer 2321 with four ports respectively coupled to the four ports 2331 -2334 of the signal combiner 2320. In Figure 19, a substantially similar signal combiner 2390 is illustrated including a balun transformer 2391 including a first coil and a second coil.

[0134] Figure 20 shows an example S-parameter (scattering parameter) matrix that can represent the example of Figure 16, and Figure 21 shows an example S-parameter matrix that can represent the example of Figures 18 and 19. One can see that the S-parameter matrix of Figure 21 is significantly different from the S-parameter matrix of Figure 20. In the example of Figure 16, an open termination at the isolation port can result in Doherty action. In the example of Figures 18 and 19, a specific termination can be provided at the isolation port to achieve Doherty action. Examples of termination are described herein in greater detail.

[0135] In some embodiments, it can be shown that such a specific termination can be implemented as a capacitance (e.g., capacitor) whose reactance is equal in magnitude to characteristic impedance of the system. Accordingly, such a capacitance can be expressed as C =1/(2 π f Z₀), where f is the operating frequency of the Doherty PA and Z₀ is a characteristic impedance of a load coupled to the Doherty PA.

[0136] Figure 22 shows an example of a Doherty combiner configuration 2400 that utilizes the hybrid circuit of Figures 18 and 19. The configuration 2400 includes a first input port 2431 which can be configured to receive a carrier-amplified signal of a Doherty PA, a second input port 2432 which can be configured to receive a peaking-amplified signal of a Doherty PA, and an output port 2433 which outputs a combination of the signals received at the first input port 2431 and the second input port 2432. The configuration 2400 includes a transformer (e.g., a balun transformer) having a first coil 2401 and a second coil 2402, the first coil 2401 implemented between a first port 241 1 and a second port 2412, the second coil 2402 implemented between a third port 2413 and a fourth port 2414. The first port 241 1 and the third port 2413 are coupled by a first capacitor 2421 and the second port 2412 and the fourth port 2414 are coupled by a second capacitor 2422. The third port 2413 is coupled to ground via a termination circuit which, in Figure 22, includes a third capacitor 2423. In some implementations, the capacitance of the first capacitor 2421 and the second capacitor 2422 are equal. In some implementations, the capacitance of the third capacitor 2423 is twice the capacitance of the first capacitor 2421 and/or the second capacitor 2422.

[0137] Impedance trajectories 2444 resulting from Doherty action in the combiner 2400 of Figure 22 are shown in Figure 23. Spread of impedance trajectories is somewhat wider than that of the example of Figure 17, but superior to the example of Figure 15. In the Doherty combiner of Figure 22, values of various performance and operating parameters are examples; and can be adjusted appropriately for different applications.

[0138] It can be shown that an alternative configuration with an inductive termination of L = ZQ/(2 π ί) can provide Doherty combiner functionality in a similar manner. Port positions of carrier and peaking amplifier can be swapped in this case. Figure 24 shows an example where such an inductive termination is utilized.

[0139] The Doherty combiner configuration 2500 of Figure 24 includes a first input port 2531 which can be configured to receive a carrier-amplified signal of a Doherty PA, a second input port 2532 which can be configured to receive a peaking- amplified signal of a Doherty PA, and an output port 2533 which outputs a combination of the signals received at the first input port 2531 and the second input port 2532. The configuration 2500 includes a transformer (e.g., a balun transformer) having a first coil 2501 and a second coil 2502, the first coil 2501 implemented between a first port 251 1 and a second port 2512, the second coil 2502 implemented between a third port 2513 and a fourth port 2514. The first port 251 1 and the third port 2513 are coupled by a first capacitor 2521 and the second port 2512 and the fourth port 2514 are coupled by a second capacitor 2522. The third port 2513 is coupled to ground via a termination circuit which, in Figure 24, includes an inductor 2523. In the Doherty combiner 2500 of Figure 24, values of various performance and operating parameters are examples; and can be adjusted appropriately for different applications.

[0140] In some embodiments, the examples described in reference to Figures 18, 19 and 20-24 can be especially useful for RFIC, MMIC and RF module (e.g., hybrid module) configurations where impedance matching is achieved by use of magnetic transformers or autotransformers. In some embodiments, a near-open output impedance of the peaking amplifier device is not inverted by the matching circuit and can be presented as such at the peaking amplifier port of a Doherty combiner.

[0141] Figure 25 shows an example of integration of a hybrid circuit having one or more features as described herein and an auto-transformer based impedance matching as an integrated passive device (IPD). The circuit 2600 includes an IPD 2602 including an impedance matching network 2610 including one or more autotransformers. The IPD further includes a combiner 2620, e.g., as described above. The circuit 2600 further includes an MMIC 2601 having a carrier amplifier 261 1 and a peaking amplifier 2612.

[0142] If an impedance inverting matching circuit is used, such as Pi- network, T-network or a quarter wave transformer, the peaking amplifier typically presents a near short impedance at the input of Doherty combiner when it is idle. In such an example, an inverted load-modulation trajectory is typically required or desired from a Doherty combiner (e.g., from 0.5^*Rload impedance to Rload impedance as shown in the example Smith chart 2744 of Figure 26). In some embodiments, such functionality can be achieved by swapping carrier and peaking amplifier inputs. Figure 27 shows an example of such a swapped configuration. Thus, in Figure 27, the circuit 2700 includes an IPD 2702 including a combiner 2720, e.g., as described above. The circuit 2700 further includes an MMIC 2701 having a carrier amplifier 271 1 and a peaking amplifier 2712. The circuit further includes an impedance inverting matching circuit 2710. Although not illustrated in Figure 27, the impedance inverting matching circuit 2710 may be implemented within the IPD 2702.

[0143] In Figures 25-27, values of various performance and operating parameters are examples; and can be adjusted appropriately for different applications.

[0144] Figure 28 shows an example architecture of a PA 2800 in which a Doherty combiner having one or more features as described herein can be implemented. The architecture shown is a Doherty PA architecture. Although the various examples are described in the context of such a Doherty PA architecture, it will be understood that one or more features of the present disclosure can also be implemented in other types of PA systems.

[0145] The example PA 2800 is shown to include an input port (RF_IN) for receiving an RF signal to be amplified. Such an input RF signal can be partially amplified by a pre-driver amplifier 2802 before being divided into a carrier amplification path 2810 and a peaking amplification path 2830. Such a division can be achieved by a divider 2804. Examples related to the divider 2804 (also referred to herein as a splitter or a power splitter) are described herein in greater detail.

[0146] In Figure 28, the carrier amplification path 2810 is shown to include an attenuator 2812 and amplification stages collectively indicated as 2814. The amplification stages 2814 are shown to include a driver stage 2816 and an output stage 2820. The driver stage 2816 is shown to be biased by a bias circuit 2818, and the output stage 2820 is shown to be biased by a bias circuit 2822. In some embodiments, there may be more or less number of amplification stages. In various examples described herein, the amplification stages 2814 are sometimes described as an amplifier; however, it will be understood that such an amplifier can include one or more stages.

[0147] In Figure 28, the peaking amplification path 2830 is shown to include phase shifting circuit 2832 and amplification stages collectively indicated as 2834. The amplification stages 2834 are shown to include a driver stage 2836 and an output stage 2840. The driver stage 2836 is shown to be biased by a bias circuit 2838, and the output stage 2840 is shown to be biased by a bias circuit 2842. In some embodiments, there may be more or less number of amplification stages. In various examples described herein, the amplification stages 2834 are sometimes described as an amplifier; however, it will be understood that such an amplifier can include one or more stages.

[0148] Figure 28 further shows that the carrier amplification path 2810 and the peaking amplification path 2830 can be combined by a combiner 2844 so as to yield an amplified RF signal at an output port (RF_OUT). Examples related to the combiner 2844 are described herein in greater detail. For example, the combiner 2844 may be implemented as one of the combiners of Figures 22 and 24.

[0149] In some implementations, a device and/or a circuit having one or more features described herein can be included in an RF device such as a wireless device. Such a device and/or a circuit can be implemented directly in the wireless device, in a modular form as described herein, or in some combination thereof. In some embodiments, such a wireless device can include, for example, a cellular phone, a smart-phone, a hand-held wireless device with or without phone functionality, a wireless tablet, etc.

[0150] Figure 29 schematically depicts an example wireless device 2900 having one or more advantageous features described herein. In the example, one or more PAs 2910 collectively indicated as a PA architecture 2101 can include one or more features as described herein. Such PAs can facilitate, for example, multi- band operation of the wireless device 2900.

[0151] The PAs 21 10a-21 10d can receive their respective RF signals from a transceiver 2910 that can be configured and operated to generate RF signals to be amplified and transmitted, and to process received signals. The transceiver 2910 is shown to interact with a baseband sub-system 2908 that is configured to provide conversion between data and/or voice signals suitable for a user and RF signals suitable for the transceiver 2910. The transceiver 2910 is also shown to be connected to a power management component 2906 that is configured to manage power for the operation of the wireless device 2900. Such power management can also control operations of the baseband sub-system 2908 and the PAs 21 10a- 21 10d.

[0152] The baseband sub-system 2908 is shown to be connected to a user interface 2902 to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system 2908 can also be connected to a memory 2904 that is configured to store data and/or instructions to facilitate the operation of the wireless device 2900, and/or to provide storage of information for the user.

[0153] In the example wireless device 2900, outputs of the PAs 21 10a- 21 10d are shown to be matched (via match circuits 2920a-2920d) and routed to an antenna 2916 via their respective duplexers 2912a-2912d and a band-selection switch 2914. The band-selection switch 2914 can be configured to allow selection of an operating band. In some embodiments, each duplexer 2912 can allow transmit and receive operations to be performed simultaneously using a common antenna (e.g., 916). In Figure 29, received signals are shown to be routed to "Rx" paths (not shown) that can include, for example, a low-noise amplifier (LNA).

[0154] A number of other wireless device configurations can utilize one or more features described herein. For example, a wireless device does not need to be a multi-band device. In another example, a wireless device can include additional antennas such as diversity antenna, and additional connectivity features such as Wi-Fi, Bluetooth, and GPS.

Power Amplification with Improved Linearization

[0155] Disclosed are various examples related to Doherty power amplifier (PA) applications, such as those for high peak to average power ratio (PAPR) 4G modulation signals used in 3G and 4G handset applications. In some embodiments, by utilizing the Doherty approach over other designs, up to 10% higher peak power added efficiency (PAE) levels can be achieved for the same adjacent power level ratio (ACLR) levels. Such PAE performance can match that of an envelope tracking (ET) PA for much less overall system complexity. [0156] Traditionally, it has been widely believed that the Doherty PA was not suitable for linear PA applications in handsets due to the size, complexity, and non-linear behavior. In fact, in base station applications, predistortion linearizers are typically used with Doherty PAs to meet linearity requirements. As described herein, issues such as size, complexity, and linearity associated with Doherty PAs can be addressed appropriately.

[0157] Figure 30 shows an example architecture of a PA 3100 having one or more features as described herein. The architecture shown is a Doherty PA architecture. Although the various examples are described in the context of such a Doherty PA architecture, it will be understood that one or more features of the present disclosure can also be implemented in other types of PA systems.

[0158] The example PA 3100 is shown to include an input port (RF_IN) for receiving an RF signal to be amplified. Such an input RF signal can be partially amplified by a pre-driver amplifier 3102 before being divided into a carrier amplification path 31 10 and a peaking amplification path 3130. Such a division can be achieved by a divider 3104. Examples related to the divider 3104 (also referred to herein as a splitter or a power splitter) are described herein in greater detail.

[0159] In Figure 30, the carrier amplification path 31 10 is shown to include an attenuator 31 12 and amplification stages collectively indicated as 31 14. The amplification stages 31 14 are shown to include a driver stage 31 16 and an output stage 3120. The driver stage 31 16 is shown to be biased by a bias circuit 31 18, and the output stage 3120 is shown to be biased by a bias circuit 3122. In some embodiments, there may be more or less number of amplification stages. In various examples described herein, the amplification stages 31 14 are sometimes described as an amplifier; however, it will be understood that such an amplifier can include one or more stages.

[0160] In Figure 30, the peaking amplification path 3130 is shown to include phase shifting circuit 3132 and amplification stages collectively indicated as 3134. The amplification stages 3134 are shown to include a driver stage 3136 and an output stage 3140. The driver stage 3136 is shown to be biased by a bias circuit 3138, and the output stage 3140 is shown to be biased by a bias circuit 3142. In some embodiments, there may be more or less number of amplification stages. In various examples described herein, the amplification stages 3134 are sometimes described as an amplifier; however, it will be understood that such an amplifier can include one or more stages.

[0161] Figure 30 further shows that the carrier amplification path 31 10 and the peaking amplification path 3130 can be combined by a combiner 3144 so as to yield an amplified RF signal at an output port (RF_OUT). Examples related to the combiner 3144 are described herein in greater detail.

[0162] Figure 31 shows an example of a combiner circuit for a Doherty PA. Such a combiner can be configured to provide moderate bandwidth performance. In Figure 31 , peaking amplifier signal and carrier amplifier signal are shown to be received from their respective collectors (not shown) and combined so as to yield an output that can be provided to, for example, a duplexer. In Figure 31 , impedance values, as well as values of various capacitance and inductance elements, are examples; and it will be understood that other values can also be implemented.

[0163] The combiner 3200 includes a first input port 321 1 (which may receive a peaking amplifier signal), a second input port 3212 (which may receive a carrier amplifier signal), and an output port 3213 that provides a combination of the signals received at the first input port 321 1 and the second input port 3212.

[0164] The first input port 321 1 is coupled to a first node 321 1 . The first node 3221 is further coupled to ground (via a first capacitor 3241 and a third inductor 3233) and to a second node 3222 (via a first inductor 3231 ). The second node 3222 is coupled to ground (via a second capacitor 3242) and a third node 3223 (via a second inductor 3232).

[0165] The second input port 3212 is coupled to a fourth node 3224. The fourth node is further coupled to ground (via a third capacitor 3243 and a fifth inductor 3235) and to a fifth node 3225 (via a fourth inductor 3234). The fifth node 3225 is coupled to ground (via a fourth capacitor 3244) and the third node 3223 (via a fifth capacitor 3245). [0166] The output port 3213 is coupled to a sixth node 3226. The sixth node 3226 is further coupled to ground (via a sixth inductor 3236) and the third node 3223 (via a sixth capacitor 3246).

[0167] The first input port 321 1 , second input port 3212, the first capacitor 3241 , the third inductor 3233, the third capacitor 3243, and the fifth inductor 3235 may be implemented as an integrated passive device (IPD). In some embodiments, the components may be implemented on a single GaAs die 3270.

[0168] The presented impedance at the second node 3222 and the fifth node 3225 may each be 25 Ohms. The presented impedance at the third node 3223 may be 12.5 Ohms.

[0169] Figure 32 shows an example of a power splitter circuit for a Doherty PA. Such a splitter can be utilized with the example combiner of Figure 31 , and be configured to provide moderate bandwidth performance. In Figure 32, an input radio-frequency (RF) signal is shown to be received at input 331 1 and be split into two paths. The first path can be coupled to a peaking PA at the first output 3312, and the second path can be coupled to a carrier PA at the second output 3313. Along the first path lies an inductor 3331 and along the second path lies a capacitor 3341 . In Figure 32, values of various capacitance and inductance elements, are examples; and it will be understood that other values can also be implemented.

[0170] Figure 33 shows an example of a power splitter 3400 that can be utilized as the divider 3104 of Figure 30. In Figure 33, the power splitter 3400 includes a transformer 3450 with two coils positioned relative to each other. The first coil can have interleaved windings that are coupled to each other, with one winding being coupled to an input 341 1 and the other winding being coupled to a first output 3414. The second coil can have interleaved windings that are coupled to each other, with one winding being coupled to an isolation port 3412 and the other winding being coupled to a second output 3413.

[0171] The example of Figure 33 can be configured as a quadrature splitter having broadband capability. Such a splitter can be configured as a semi- lumped 90 degree power divider that can be implemented as IPD design for low frequencies and also as an integrated divider on GaAs die for higher frequencies. [0172] The power splitter 3400 can further include capacitors 3441 , 3442 coupling the coils. In some embodiments, a first capacitor 3441 is coupled between the input 341 1 and the isolation port 3412 and a second capacitor 3442 is coupled between the first output 3413 and the second output 3414.

[0173] With the foregoing configuration, power of an RF signal received at the input port can be split into the two output ports 3413, 3414. Such split signals can be provided to the carrier amplifier and peaking amplifier of Figure 30.

[0174] Figure 34 shows an example of a power splitter 3500 that can be utilized as the divider 3104 of Figure 1 . Additional details concerning such a power splitter are described above, including but not limited to the section entitled "Power Amplification Using a Balun Transformer".

[0175] The example of Figure 34 can be configured as a quadrature splitter having broadband capability. In some embodiments, such a splitter can be configured as a lumped 90 degree power divider that can be implemented as an SMT circuit for low frequencies, and also as an integrated (e.g., IPD) divider on GaAs die for higher frequencies.

[0176] Figure 35 shows an example of a combiner 3600 that can be utilized as the combiner 3144 of Figure 30. Additional details concerning such a combiner are described above, including but not limited to the section entitled "Power Amplification Using a Balun Transformer".

[0177] The example of Figure 35 can be implemented as an SMT circuit having broadband capability. In some embodiments, such a combiner can include power combining and dynamic load pulling functionalities implemented with use of a lumped balun.

[0178] Figure 36 shows another example of a combiner 3700 that can be utilized as the combiner 3144 of Figure 30. Additional details concerning such a combiner are described above, including to but not limited to the section entitled "Signal Combining using a Coiled Balun Transformer".

[0179] The example of Figure 36 can be implemented as an IPD having broadband capability. In some embodiments, such a combiner can include power combining and dynamic load pulling functionalities implemented with use of a semi- lumped 90 degree hybrid configuration.

[0180] Referring to Figure 30, in some embodiments, each of the driver stage 31 16 and the output stage 3120 of the carrier amplifier 31 14 can be configured to operate in a Class AB mode. Further, each of the driver stage 3136 and the output stage 3140 of the peaking amplifier 3134 can be configured to operate in a Class B mode. For such configurations, bias circuits such as those shown in Figures 38 and 39 can be utilized to bias the stages of the carrier amplifier 31 14 and peaking amplifier 3134, respectively. Thus, the carrier amplifier 31 14 and the peaking amplifier 3134 may operate in different biasing modes. Further, for each amplifier 31 14, 3134, each stage (31 16, 3120 and 3136, 3140) may operate in different biasing modes. The different biasing modes can include Class A, Class B, Class AB, Class C, Class D, Class F, Class G, Class I, Class S, Class T, or any other biasing mode.

[0181] Figure 37 shows an example of a low headroom Class AB bias circuit that can be utilized to provide a bias voltage (VBIAS) to a stage (driver 31 16 or output 3120) of the carrier amplifier 31 14. Accordingly, the Class AB bias circuit can provide the biasing functionality of the bias circuit 31 18 and/or the bias circuit 3122 of Figure 30. Appropriate selections of transistors, diodes, capacitances and resistances can be implemented to accommodate such driver and output stage functionalities. In some embodiments, the example bias circuit of Figure 37 can be particularly suitable for integration with external band gap references on CMOS or GaAs where low voltage headroom makes use of conventional 2xVbe bias circuits difficult. The bias circuit of Figure 37 can include sufficient bandwidth at baseband frequencies to support broad band signals such as LTE.

[0182] Figure 38 shows an example of a low headroom Class B bias circuit that can be utilized to provide a bias voltage (VBIAS) to a stage (driver 3136 or output 3140) of the peaking amplifier 3134. Accordingly, the Class B bias circuit can provide the biasing functionality of the bias circuit 3138 and/or the bias circuit 3142 of Figure 30. Appropriate selections of transistors, diodes, capacitances and resistances can be implemented to accommodate such driver and output stage functionalities.

[0183] Figure 39 shows an example of a beneficial effect of utilizing a Class B biasing of the driver stage for the peaking amplifier (3134 in Figure 1 ). The graph 4000 of Figure 39 includes plots of output stage current as a function of output power for different configurations. For the carrier amplifier, the solid line 401 1 is for a configuration where each of the driver and output stages is biased in a Class B mode, while the dashed line 401 1 is for a configuration with Class AB biasing of the driver stage and Class B biasing of the output stage. Similarly, for the peaking amplifier, the solid line 4021 is for a configuration where each of the driver and output stages is biased in a Class B mode, while the dashed line 4022 is for a configuration with Class AB biasing of the driver stage and Class B biasing of the output stage. As shown in Figure 39, the use of Class B biasing in the driver stage in the peaking amplifier greatly reduces the current consumption of the output stage. However, the use of Class B biasing in the driver stage in the carrier amplifier slightly increases the current consumption of the output stage.

[0184] Figure 40 shows an example of a beneficial effect of utilizing a Class B biasing of the driver stage for the peaking amplifier (3134 in Figure 1 ). The graph 4100 of Figure 40 includes plots of power-added efficiency (PAE) as a function of output power for different configurations. The solid line 4101 is for a configuration where each of the driver and output stages of the peaking amplifier is biased in a Class B mode. The dashed line 4102 is for a configuration where the driver stage is biased in a Class AB mode, and the output stage is biased in a Class B mode. The dash-dash line 4103 is for an equivalent non-Doherty amplifier biased in a Class AB mode. As shown in Figure 40, the use of Class B biasing in the driver stage in the peaking amplifier increases the PAE performance significantly.

[0185] Figure 41 shows an example of linearization effect that can be obtained by introducing a phase shift between the RF signals associated with the carrier amplification and peaking amplification. Such a phase shift can be introduced by, for example, the phase shift component 3132 of Figure 1 . The graph 1200 of Figure 41 includes plots of AM/AM (left vertical axis) and AM/PM (right vertical axis) as a function of output power. For the AM/AM plots 421 1 , 4212, Figure

41 shows that the curve corresponding to a configuration with a phase shift has less AM/AM distortion, especially at higher output power, than a configuration without phase shift. Similarly, for the AM/PM plots 4221 , 4222, Figure 41 shows that the curve corresponding to a configuration with a phase shift has less AM/PM distortion, especially at higher output power, than a configuration without phase shift.

[0186] As described herein, power split into the carrier amplification path and the peaking amplification path can be different. Figure 42 shows an example of linearization effect that can be obtained by introducing such an uneven power split between the RF signals associated with the carrier amplification and peaking amplification. Such an uneven power split can be introduced by or be facilitated by, for example, the attenuator component 31 12 of Figure 1 . The graph 4300 of Figure

42 includes plots of AM/AM (left vertical axis) and AM/PM (right vertical axis) as a function of output power. For the AM/AM plots 431 1 , 4312, Figure 42 shows that the curve corresponding to a configuration with an uneven power split has less AM/AM distortion, especially at higher output power, than a configuration with an even power split configuration. Similarly, for the AM/PM plots 1321 , 1322, Figure 13 shows that the curve corresponding to a configuration with an uneven power split has less AM/PM distortion, especially at mid to higher output power, than a configuration with an even power split configuration.

[0187] Figure 43 shows an example of combined linearization effect that can be obtained by a combination of the foregoing phase shift and uneven power split features described in reference to Figures 41 and 42. The graph 4400 of Figure

43 includes plots of gain (left vertical axis) and PAE (right vertical axis) as a function of output power. In particular, line 441 1 shows the gain for a non-Doherty amplifier, line 4412 shows the gain for a Doherty amplifier without phase shift and even power split, and line 4413 shows the gain for Doherty amplifier with phase shift and uneven power split. Similarly, line 4421 shows the PAE for a non-Doherty amplifier, line 4412 shows the PAE for a Doherty amplifier without phase shift and even power split, and line 4413 shows the PAE for Doherty amplifier with phase shift and uneven power split. [0188] Figure 43 shows that the linear load modulated amplifier (Doherty PA with phase shift and uneven power split) has a gain compression curve that is very similar to that of a non-Doherty PA (e.g., Class AB/F amplifier). Figure 43 also shows that the PAE of the linear load modulated amplifier (Doherty PA with phase shift and uneven power split) is only slightly less (e.g., about 3% less at higher output power) than that of a classic non-linear Doherty amplifier (Doherty PA with no linearization).

[0189] Figure 44 shows plots of PAE (left vertical axis) and adjacent channel power (ACP) (right vertical axis) at various operating frequencies for a front- end module (FEM) having a dual-band Doherty PA configured for LTE operation, and an FEM having an average power tracking (APT) PA. Figure 44 shows that the PAE is generally higher, and the magnitude of ACP is generally lower, for the Doherty PA than the APT PA. In the example shown, the improvement is about 10%.

[0190] In some implementations, a device and/or a circuit having one or more features described herein can be included in an RF device such as a wireless device. Such a device and/or a circuit can be implemented directly in the wireless device, in a modular form as described herein, or in some combination thereof. In some embodiments, such a wireless device can include, for example, a cellular phone, a smart-phone, a hand-held wireless device with or without phone functionality, a wireless tablet, etc.

[0191] Figure 45 schematically depicts an example wireless device 3801 having one or more advantageous features described herein. In the example, one or more PAs 31 10a-31 10d collectively indicated as a PA architecture 3101 can include one or more features as described herein. Such PAs can facilitate, for example, multi-band operation of the wireless device 3801 .

[0192] The PAs 31 10a-31 10d can receive their respective RF signals from a transceiver 3810 that can be configured and operated to generate RF signals to be amplified and transmitted, and to process received signals. The transceiver 3810 is shown to interact with a baseband sub-system 3808 that is configured to provide conversion between data and/or voice signals suitable for a user and RF signals suitable for the transceiver 3810. The transceiver 3810 is also shown to be connected to a power management component 3806 that is configured to manage power for the operation of the wireless device 3801 . Such power management can also control operations of the baseband sub-system 3808 and the PAs 31 10a- 31 10d.

[0193] The baseband sub-system 3808 is shown to be connected to a user interface 3802 to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system 3808 can also be connected to a memory 3404 that is configured to store data and/or instructions to facilitate the operation of the wireless device 3801 , and/or to provide storage of information for the user.

[0194] In the example wireless device 3801 , outputs of the PAs 31 10a- 31 10d are shown to be matched (via match circuits 3820a-3820d) and routed to an antenna 3816 via their respective duplexers 3812a-3812d and a band-selection switch 3814. The band-selection switch 3814 can be configured to allow selection of an operating band. In some embodiments, each duplexer 3812 can allow transmit and receive operations to be performed simultaneously using a common antenna (e.g., 3816). In Figure 45, received signals are shown to be routed to "Rx" paths (not shown) that can include, for example, a low-noise amplifier (LNA).

[0195] A number of other wireless device configurations can utilize one or more features described herein. For example, a wireless device does not need to be a multi-band device. In another example, a wireless device can include additional antennas such as diversity antenna, and additional connectivity features such as Wi-Fi, Bluetooth, and GPS.

[0196] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." The word "coupled", as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Description using the singular or plural number may also include the plural or singular number respectively. The word "or" in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0197] The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times.

[0198] The teachings of the invention provided herein can be applied to other systems, not necessarily the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments.

[0199] While some embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.

Claims

WHAT IS CLAIMED IS:

1 . A power amplifier (PA) system comprising:

an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion;

a Doherty amplifier circuit including a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion; and

an output circuit coupled to the Doherty amplifier circuit, the output circuit including a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal.

2. The PA system of claim 1 further comprising a pre-driver amplifier configured to partially amplify the RF signal before reception by the input circuit.

3. The PA system of claim 2 wherein at least one of the input circuit and the output circuit is implemented as a lumped-element circuit.

4. The PA system of claim 2 wherein the carrier amplification path includes a carrier amplifier and the peaking amplification path includes a peaking amplifier, each of the carrier amplifier and the peaking amplifier including a driver stage and an output stage.

5. The PA system of claim 4 wherein the input circuit includes a modified Wilkinson power divider configured to provide DC power to each of the carrier amplifier and the peaking amplifier.

6. The PA system of claim 5 wherein the DC power is provided to the carrier amplifier and the peaking amplifier through a choke inductance.

7. The PA system of claim 5 wherein each of the carrier amplification path and the peaking amplification path includes a DC blocking capacitance.

8. The PA system of claim 5 wherein the modified Wilkinson power divider is further configured to provide impedance matching between the driver stages and the pre-driver amplifier.

9. The PA system of claim 8 wherein each of the carrier amplification path and the peaking amplification path includes an LC matching circuit having a capacitance along the path and an inductive coupling to ground.

10. The PA system of claim 5 wherein the modified Wilkinson power divider is configured to provide a desired phase shifting to compensate or tune for an AM-PM effect associated with the peaking amplifier.

1 1 . The PA system of claim 5 wherein the modified Wilkinson power divider is further configured to provide a desired attenuation adjustment at an input of either the carrier amplifier or the peaking amplifier to compensate or tune for an AM-AM effect associated with the carrier amplifier and the peaking amplifier.

12. The PA system of claim 1 1 wherein the modified Wilkinson power divider includes a capacitance that couples a first node along the carrier amplification path to a ground, and an impedance that couples a second node along the peaking amplification path to the ground.

13. The PA system of claim 12 wherein the modified Wilkinson power divider further includes an isolation resistance implemented between the first node and the second node, the isolation resistance selected to prevent or reduce a source-pulling effect between the carrier amplification path and the peaking amplification path.

14. The PA system of claim 4 wherein the BALUN circuit includes an LC BALUN transformer.

15. The PA system of claim 14 wherein the peaking amplifier is configured to behave as a short circuit or a low impedance node when in an off state, and the carrier amplifier is configured to behave as a single-ended amplifier equivalent to that of a single-section matching network having a series inductance and a shunt capacitance when utilizing the LC BALUN transformer.

16. The PA system of claim 15 wherein the LC BALUN transformer is configured such that an impedance seen by the carrier amplifier is increased when in a low power mode.

17. The PA system of claim 16 wherein the impedance seen by the carrier amplifier is approximately doubled when in the low power mode.

18. The PA system of claim 15 wherein the peaking amplifier is further configured to operate in a similar manner as a push-pull amplifier where an RF current from the carrier amplifier is influenced by an RF current from the peaking amplifier.

19. The PA system of claim 18 wherein the push-pull operation reduces even-harmonics thereby improving linearity.

20. The PA system of claim 14 wherein the LC BALUN transformer includes a first path that couples an output of the carrier amplifier to an output node, and a second path that couples an output of the peaking amplifier to the output node.

21 . The PA system of claim 20 wherein each of the first path and the second path is inductively coupled to a DC port to provide a DC feed to the output stage.

22. The PA system of claim 20 wherein each of the first path and the second path includes a harmonic trap.

23. The PA system of claim 22 wherein the harmonic trap includes a second harmonic trap having an LC shunt to ground and a series inductance.

24. The PA system of claim 20 wherein the second path includes a shunt capacitance and a series capacitance configured to provide phase compensation for the output of the peaking amplifier.

25. The PA system of claim 24 wherein at least one of the shunt capacitance and the series capacitance is a surface-mount technology (SMT) capacitor.

26. The PA system of claim 14 wherein the LC BALUN transformer is configured to provide reduced loss in the carrier amplification path to maintain high efficiency at back-off and in a high power mode.

27. The PA system of claim 4 wherein load modulation of the peaking amplifier is configured such that an impedance loci for the peaking amplifier run from an approximately short circuit when the peaking amplifier is in an off state to an optimum load impedance when the peaking amplifier is contributing approximately same power as the carrier amplifier.

28. The PA system of claim 4 wherein the input circuit is a broadband circuit at least in part due to a lead-lag network configured to provide broadband phase shift.

29. The PA system of claim 4 wherein the input circuit is configured to provide reactive to real impedance matching, and isolation between the carrier amplifier and peaking amplifier, while providing broadband performance.

30. A method for amplifying a radio-frequency (RF) signal, the method comprising:

providing a Doherty amplifier circuit having a carrier amplification path and a peaking amplification path;

receiving an RF signal;

splitting the RF signal into a first portion and a second portion, the first portion provided to the carrier amplification path, the second portion provided to the peaking amplification path; and

combining, using a balance to unbalance (BALUN) circuit, outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal.

31 . A power amplifier module comprising:

a packaging substrate configured to receive a plurality of components; a power amplifier (PA) system implemented on the packaging substrate, the PA system including an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion, the PA system further including a Doherty amplifier circuit having a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second, the PA system further including an output circuit coupled to the Doherty amplifier circuit, the output circuit including a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal; and

a plurality of connectors configured to provide electrical connections between the PA system and the packaging substrate.

32. A wireless device comprising:

a transceiver configured to generate a radio-frequency (RF) signal; a power amplifier (PA) module in communication with the transceiver, the PA module including an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion, the PA module further including a Doherty amplifier circuit having a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion, the PA module further including an output circuit coupled to the Doherty amplifier circuit, the output circuit including a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal; and an antenna in communication with the PA module, the antenna configured to facilitate transmission of the amplified RF signal.

33. A signal combiner comprising:

a balun transformer circuit having a first coil and a second coil, the first coil implemented between a first port and a second port, the second coil implemented between a third port and a fourth port, the first port and the third port coupled by a first capacitance, the second port and the fourth port coupled by a second capacitance, the first port configured to receive a first signal, the fourth port configured to receive a second signal, the second port configured to yield a combination of the first signal and the second signal; and a termination circuit that couples the third port to a ground.

34. The signal combiner of claim 33 wherein the first port is configured to receive a carrier-amplified signal from a Doherty power amplifier (PA) and the fourth port is configured to receive a peaking-amplified signal from the Doherty PA.

35. The signal combiner of claim 34 wherein the termination circuit includes a capacitor.

36. The signal combiner of claim 35 wherein the capacitor has a capacitance approximately equal to a multiplicative inverse of two times pi times an operating frequency of the Doherty PA times a characteristic impedance of a load coupled to the Doherty PA.

37. The signal combiner of claim 33 wherein the first port is configured to receive a peaking-amplified signal from a Doherty power amplifier (PA) and the fourth port is configured to receive a carrier-amplified signal from the Doherty PA.

38. The signal combiner of claim 37 wherein the termination circuit includes an inductor.

39. The signal combiner of claim 38 wherein the inductor has an inductance approximately equal to a characteristic impedance of a load coupled to the Doherty PA divided by two time pi times an operating frequency of the Doherty PA.

40. The signal combiner of claim 33 wherein an S-parameter between a first one of the ports and a second one of the ports is approximately equal to (1 +j)/2.

41 . The signal combiner of claim 33 wherein an S-parameter between a first one of the ports and second one of the ports is approximately equal to (1 -j)/2.

42. The signal combiner of claim 33 wherein an S-parameter matrix of S- parameters between the ports only includes values of approximately 0, (1 +j)/2, and (1 -j)/2.

43. The signal combiner of claim 33 wherein the balun transformer circuit is implemented as an integrated passive device.

44. The signal combiner of claim 43 wherein the integrated passive device further implements an auto-transformer based impedance matching circuit.

45. A power amplifier (PA) module comprising:

a packaging substrate configured to receive a plurality of components; and

a signal combiner implemented on the packaging substrate, the signal combiner including a balun transformer circuit having a first coil and a second coil, the first coil implemented between a first port and a second port, the second coil implemented between a third port and a fourth port, the first port and the third port coupled by a first capacitance, the second port and the fourth port coupled by a second capacitance, the first port configured to receive a first signal, the fourth port configured to receive a second signal, the second port configured to yield a combination of the first signal and the second signal, the signal combiner further including a termination circuit that couples the third port to a ground.

46. The PA module of claim 45 wherein the balun transformer circuit is implemented as an integrated passive device.

47. The PA module of claim 46 wherein the integrated passive device further implements an auto-transformer based impedance matching circuit.

48. The PA module of claim 45 wherein the PA module further includes a Doherty PA implemented on the packaging substrate, the Doherty PA having a carrier amplification path yielding a carrier-amplified signal and a peaking amplification path yielding a peaking-amplified signal.

49. The PA module of claim 48 wherein the first port is configured to receive the carrier-amplified signal and the fourth port is configured to receive the peaking-amplified signal.

50. The PA module of claim 49 wherein the termination circuit includes a capacitor having a capacitance approximately equal to a multiplicative inverse of two times pi times an operating frequency of the Doherty PA times a characteristic impedance of a load coupled to the Doherty PA.

51 . The PA module of claim 48 wherein the first port is configured to receive the peaking-amplified signal and the fourth port is configured to receive the carrier-amplified signal.

52. The PA module of claim 51 wherein the termination circuit includes an inductor having an inductance approximately equal to a characteristic impedance of a load coupled to the Doherty PA divided by two time pi times an operating frequency of the Doherty PA.

53. The PA module of claim 45 wherein an S-parameter matrix of S- parameters between the ports only includes values of approximately 0, (1 +j)/2, and (1 -j)/2.

54. A wireless device comprising:

a transceiver configured to generate a radio-frequency (RF) signal; a power amplifier (PA) module in communication with the transceiver, the PA module including an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion, the PA module further including a Doherty PA having a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion, the PA module further including an output circuit coupled to the Doherty amplifier circuit, the output circuit including a balun transformer circuit having a first coil and a second coil, the first coil implemented between a first port and a second port, the second coil implemented between a third port and a fourth port, the first port and the third port coupled by a first capacitance, the second port and the fourth port coupled by a second capacitance, the first port configured to receive a first signal via the carrier amplification path, the fourth port configured to receive a second signal via the peaking amplification path, the second port configured to yield a combination of the first signal and the second signal as an amplified RF signal; and

an antenna in communication with the PA module, the antenna configured to facilitate transmission of the amplified RF signal.

55. A method for amplifying a radio-frequency (RF) signal, the method comprising:

receiving an RF signal;

combining, using a balun transformer circuit, an output of the carrier amplification path and an output of the peaking amplification path to yield an amplified RF signal, the balun transformer circuit having a first coil and a second coil, the first coil implemented between a first port and a second port, the second coil implemented between a third port and a fourth port, the first port and the third port coupled by a first capacitance, the second port and the fourth port coupled by a second capacitance, the first port configured to receive the output of the carrier amplification path, the fourth port configured to receive the output of the peaking amplification path, and the second port configured to yield the amplified RF signal.

56. A power amplifier (PA) system comprising:

a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion, the first portion and the second portion having different phases and different powers; and

an output circuit coupled to the Doherty amplifier circuit, the output circuit configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal.

57. The PA system of claim 56 wherein the input circuit includes a phase- shifter configured to cause the first portion and the second portion to have different phases.

58. The PA system of claim 57 wherein the phase-shifter and peaking amplifier are implemented in a peaking amplification path.

59. The PA system of claim 56 wherein the first portion and second portion are out-of-phase by between 10 degrees and 20 degrees.

60. The PA system of claim 56 wherein the different phases reduce at least one of AM/AM distortion or AM/PM distortion as compared to equal phases.

61 . The PA system of claim 56 wherein the input circuit includes an attenuator configured to cause the first portion and the second portion to have different powers.

62. The PA system of claim 61 wherein the attenuator and the carrier amplifier are implemented in a carrier amplification path.

63. The PA system of claim 56 wherein the different powers reduce at least one of AM/AM distortion or AM/PM distortion as compared to equal powers.

64. The PA system of claim 56 wherein the input circuit includes a pre- driver amplifier.

65. The PA system of claim 56 wherein the peaking amplifier includes a driver stage configured to operate in a first biasing mode and an output stage configured to operate in a first biasing mode.

66. The PA system of claim 65 wherein the first biasing mode is a Class B biasing mode.

67. The PA system of claim 56 wherein the Class B biasing mode increases the PAE of the peaking amplifier as compared to a Class AB biasing mode.

68. The PA system of claim 65 wherein the carrier amplifier includes a driver stage configured to operate in a second biasing mode.

69. The PA system of claim 68 wherein the second biasing mode is a Class AB biasing mode.

70. The PA system of claim 68 wherein the carrier amplifier further includes an output stage configured to operate in the first biasing mode.

71 . The PA system of claim 68 wherein the carrier amplifier further includes an output stage configured to operate in the second biasing mode.

72. A power amplifier (PA) module comprising: a packaging substrate configured to receive a plurality of components; and

a PA system implemented on the packaging substrate, the PA system including an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion, a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion, the first portion and the second portion having different phases and different powers, and an output circuit coupled to the Doherty amplifier circuit, the output circuit configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal.

73. The PA module of claim 72 wherein at least one of the input circuit or the output circuit is implemented as an integrated passive device.

74. The PA module of claim 72 wherein at least one of the input circuit or the output circuit is implemented on a single GaAs die.

75. A wireless device comprising:

a transceiver configured to generate a radio-frequency (RF) signal; a power amplifier (PA) module in communication with the transceiver, the PA module including an input circuit configured to receive the RF signal and split the RF signal into a first portion and a second portion, a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion, the first portion and the second portion having different phases and different powers, and an output circuit coupled to the Doherty amplifier circuit, the output circuit configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal; and an antenna in communication with the PA module, the antenna configured to facilitate transmission of the amplified RF signal.

76. A method for amplifying a radio-frequency (RF) signal, the method comprising:

receiving an RF signal;

splitting the RF signal into a first portion and a second portion, the first portion provided to the carrier amplification path, the second portion provided to the peaking amplification path, the first portion and the second portion having different phases and different powers; and

combining an output of the carrier amplification path and an output of the peaking amplification path to yield an amplified RF signal.